The genus Euonymus is a large group of plants composed of shrubs, vines and ground covers, according to Clemson University. These can vary widely in appearance and even growth. Some are evergreen, while others are deciduous. The most popular with home gardeners are the evergreen shrubs, such as the attractive Euonymus japonicus. Unfortunately, these shrubs are often overused in the landscape and can become highly susceptible to common diseases.
Cercospora Leaf Spot
This is a fungal disease of Euonymus plants, meaning it is caused by one or more types of fungi. This particular disease, which is rather common according to Clemson University, is caused by either the Cercospora detructiva fungus, the C. euonymi fungus or both. The primary symptom of the disease is the appearance of small brown marks on the leaves. They can appear as pinpricks or as splotches. Over time, the spots grow, move together and spread, covering the leaves. Sometimes, the middle of the brown areas becomes greasy and gray in color. In other cases, the spots drop out of the leaves, or the leaves shrivel up and drop off the plant.
Although this disease is unattractive, it is not life-threatening. Any dropped leaves should be removed immediately, as the fungi can overwinter in the soil. You can use a fungicidal spray to treat the plant. Make sure the ingredients contain thiophanate-methyl, and follow the instructions on the label for the size and age of your Euonymus plant.
Euonymus plants are highly susceptible to crown gall, which is a disease caused by several different types of bacterium. The primary symptom is the development of large, round galls, which swell up on the branches of the plant. Affected areas of the plant can be pruned off if the galls are limited to one area. Otherwise, you can ignore the disease, as it is not life-threatening, according to the University of Missouri. Still, it is unattractive. Prevent crown gall by guarding against insect infestations of the Euonymus, as the bacteria that cause crown gall can enter the plant on the bodies of insects. Spray the plant with an insecticide if you notice increased insect activity on your shrub.
Anthracnose is a disease that affects a wide range of woody ornamental plants, including those in the Euonymus family. This is a fungal disease, but instead of infecting only the leaves, the fungi, which are from the Colletrotichum species, attack the wood as well. Symptoms include brown spots on the leaves and dark, sunken, cracked areas of wood. As a result, Euonymus shrubs often lose their leaves, even those that are evergreen.
Prune off infected areas and remove any dropped leaves from the soil. Begin a systematic fungicidal treatment to prevent Anthracnose from harming your Euonymus and other woody plants. Look for a fungicide marketed as "all purpose" or "garden treatment" and apply it at regular intervals, starting in early spring, according to the directions on the package. Anthracnose can be fatal in severe cases, especially if the plant is stressed from environmental conditions.